Novel pumping apparatus

ABSTRACT

A compact pumping system especially useful in liquid chromatography wherein comprising a liquid path which is fully flushed on each stroke of a pump, a pump which provides substantially pulse-free flow, a pressure-sensor integrated into said flow path and operably connected to the control circuit of a bifilar stepping motor. This circuit is so designed that the driving current applied to the motor is only that required to pump the liquid. The avoiding of heat associated with a greater current is particularly important in forming a compact package of motor and pump for use in liquid chromatography.



1. In a chromatography system of the type comprising (A) a liquid delivery system comprising a pump and discharge port for supplying liquid under pressure to (B) a compartment containing a stationary phase forming means to interact with said liquid phase to effect a separation thereof during its passage through said compartment, and (C) means to collect the liquid phase leaving the compartment, the improvement wherein said liquid delivery system comprises
 1. interposed between said pump and said compartment, a liquid pressure-sensing means, and
 2. motor control means operably communicating between said pressure-sensing means and a motor drive means for said pump, said motor control means forming means to control the flowoutput of said pump by controlling said motor in response to the pressure-sensed by said pressure-sensing means.
 2. motor control means operably communicating between said pressure-sensing means and a motor drive means for said pump, said motor control means forming means to control the flow-output of said pump by controlling said motor in response to the pressure-sensed by said pressure-sensing means.
 2. A system as defined in claim 1 wherein the output of said motor is substantially continuously controlled in response to a liquid pressure between said pump and said compartment.
 3. A system as defined by claim 2 wherein said motor in a stepping motor and said control means controls the current applied to drive said motor.
 4. A system as defined in claim 1 wherein said motor control means comprises additional control means to modify motor output in response to pressure, said additional control means forming means to compensate for compression of said liquid being pumped, and to maintain a substantially constant input of liquid into said column despite changes in compression of said liquid with varying pressure.
 5. A system as defined in claim 4 wherein said pump comprises a two-cylinder piston pump and wherein said pump is operated by a drive forming means to operate the piston in each said cylinder by driving a centrally-located member which, in turn, forms means to simultaneously turn two non-circular members 180* out of phase with each other, each said non-circular member forming means to operate a piston in each said cylinder and thereby provide means for achieving a substantially constant discharge of liquid from said pump.
 6. A system as defined in claim 5 wherein substantially all liquid-receptive volume between inlet of said pump cylinder and discharge port from said cylinder is flushed by each cycle of said piston.
 7. Apparatus as defined in claim 5 wherein there are two check valves mounted in series at both inlet and outlet ports of each said cylinder.
 8. A system as defined by claim 4 wherein said motor is a stepping motor and said motor control means controls the current applied to drive said motor.
 9. A system as defined in claim 1 wherein said pump comprises a two-cylinder piston pump and wherein said pump is operated by a drive forming means to operate the piston in each said cylinder by driving a centrally-located member which, in turn, forms means to simultaneously turn two non-circular members 180* out of phase with each other, each said non-circular member forming means to operate a piston in each said cylinder and thereby provide means for achieving a substantially constant discharge of liquid from said pump.
 10. A system as defined by claim 9 wherein said motor is a stepping motor and said motor control means controls the current applied to drive said motor.
 11. A system as defined in claim 9 wherein substantially all liquid-receptive volume between inlet of a said pump cylinder and discharge port from said cylinder is flushed by each cycle of said piston.
 12. Apparatus as defined in claim 9 wherein said pump comprises a plurality of cylinders, a plunger in each cylinder, a liquid inlet to each cylinder proximate the end of said plunger as positioned at the end of its forward stroke, a liquid outlet to said cylinder proximate the end of said plunger as positioned at the backward stroke, and an annular conduit between said plunger and said cylinder forming means for said liquid to reach said liquid outlet in response to the forward movement of said plunger.
 13. Apparatus as defined in claim 12 wherein said annular conduit is from 0.001 to 0.005 inches in width.
 14. Apparatus as defined in claim 12 wherein said motor is a stepping motor and said control means controls the current applied to drive said motor.
 15. Apparatus as defined in claim 9 wherein said pump comprises a plurality of cylinders, a piston in each cylinder, a liquid inlet to each cylinder proximate the end of said piston as positioned at the end of its forward stroke, a liquid outlet to said cylinder proximate the end of said piston as positioned at the backward stroke, and an annular conduit between said piston and said cylinder forming means for said liquid to reach said liquid outlet in response to the forward movement of said piston.
 16. Apparatus as defined in claim 15 wherein the liquid''s flow path is no more than about 0.2 inches from the mean center line of said flow path.
 17. Apparatus as defined in claim 9 wherein the liquid''s flow path is no more than about 0.2 inches from the mean center line of said flow path.
 18. Apparatus as defined in claim 17 wherein there are two check valves mounted in series at both inlet and outlet ports of each said cylinder.
 19. Apparatus as defined in claim 9 wherein there are two check valves mounted in series at both inlet and outlet ports of each said cylinder.
 20. In a system of the type defined in claim 1, the improvement wherein said flow-control means comprises A) Bourdon-type tube, the interior of which forms a flow path for said liquid B) means for sensing displacement of said tube in response to pressure of the liquid therein, and C) motor control means comprising said sensing means and a motor drive means for said pump.
 21. A system of the type defined in claim 20 wherein said Bourdon-type tube is enclosed within a housing and mounted between a light source and a light-sensing means, said light source and sensing means forming said displacement-sensing means, and also forming means to provide an input signal to said motor control means.
 22. A system as defined by claim 21 wherein said motor is a stepping motor and said motor control means controls the current applied to drive said motor.
 23. Apparatus as defined in claim 21 wherein the liquid''s flow path is no more than about 0.2 inches from the mean center line of said flow path.
 24. A system of the type defIned in claim 20 wherein said Bourdon tube is bent to form two substantially parallel segments of a single conduit.
 25. A system as defined in claim 20 wherein substantially all liquid-receptive volume between inlet of a said pump cylinder and discharge port from said cylinder is flushed by each cycle of said piston.
 26. A system as defined in claim 20 wherein said flow path of said Bourdon-type tube has an inside diameter of from about 0.005 inches to 0.10 inches.
 27. A system as defined in claim 1 wherein said control means forms means to controllably drive said motor over a speed ratio of about 100:1 or greater.
 28. Apparatus as defined in claim 1 wherein said pump comprises a plurality of cylinders, a piston in each cylinder, a liquid inlet to each cylinder proximate the end of said piston as positioned at the end of its forward stroke, a liquid outlet to said cylinder proximate the end of said piston as positioned at the backward stroke, and an annular conduit between said piston and said cylinder forming means for said liquid to reach said liquid outlet in response to the forward movement of said piston.
 29. Apparatus as defined in claim 28 wherein the liquid''s flow path is no more than about 0.2 inches from the mean center line of said flow path.
 30. In a system as defined in claim 1 suitable for handling heat sensitive liquids, and said motor and said pump being mounted adjacent one another, the improvement wherein said motor is a stepping motor system comprising a control means for controlling the volume output of said pump by controlling the driving current applied to the coils of said motor.
 31. A liquid delivery system as defined in claim 30 wherein said motor has an operating range which is substantially free of resonance effects and is 100:1 or greater. 